.\" $OpenBSD: pthread_getconcurrency.3,v 1.4 2013/06/05 03:44:50 tedu Exp $
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.\" Copyright (c) 2003 Sergey Osokin <osa@FreeBSD.org.ru>
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.\" $FreeBSD: src/lib/libc_r/man/pthread_getconcurrency.3,v 1.2 2003/05/24 19:50:43 ru Exp $
.Dd $Mdocdate: June 5 2013 $
.Dt PTHREAD_GETCONCURRENCY 3
.Os
.Sh NAME
.Nm pthread_getconcurrency ,
.Nm pthread_setconcurrency
.Nd get or set level of concurrency
.Sh SYNOPSIS
.In pthread.h
.Ft int
.Fn pthread_getconcurrency void
.Ft int
.Fn pthread_setconcurrency "int new_level"
.Sh DESCRIPTION
The
.Fn pthread_setconcurrency
function allows an application to inform the threads implementation
of its desired concurrency level,
.Fa new_level .
The actual level of concurrency provided by the implementation
as a result of this function call is unspecified.
If
.Fa new_level
is zero, it causes the implementation to maintain the concurrency
level at its discretion as if
.Fn pthread_setconcurrency
was never called.
The
.Fn pthread_getconcurrency
function returns the value set by a previous call to the
.Fn pthread_setconcurrency
function.
If the
.Fn pthread_setconcurrency
function was not previously called, this function returns zero to
indicate that the implementation is maintaining the concurrency
level.
When an application calls
.Fn pthread_setconcurrency ,
it is informing the implementation of its desired concurrency
level.
The implementation uses this as a hint, not a requirement.
.Sh RETURN VALUES
If successful, the
.Fn pthread_setconcurrency
function returns zero.
Otherwise, an error number is returned
to indicate the error.
The
.Fn pthread_getconcurrency
function always returns the concurrency level set by a previous
call to
.Fn pthread_setconcurrency .
If the
.Fn pthread_setconcurrency
function has never been called,
.Fn pthread_getconcurrency
returns zero.
.Sh ERRORS
.Fn pthread_setconcurrency
will fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
The value specified by
.Fa new_level
is negative.
.It Bq Er EAGAIN
The value specified by
.Fa new_level
would cause a system resource to be exceeded.
.El
.Sh APPLICATION USAGE
Use of these functions changes the state of the underlying
concurrency upon which the application depends.
Library developers are advised to not use the
.Fn pthread_getconcurrency
and
.Fn pthread_setconcurrency
functions since their use may conflict with an application's
use of these functions.
.Sh STANDARDS
The
.Fn pthread_getconcurrency
and
.Fn pthread_setconcurrency
functions conform to
.St -susv2 .
